Improving thermal insulation of concrete sandwich panel buildings

Improving thermal insulation of

concrete sandwich panel buildings

Jørgen Munch-Andersen

Danish Building Research Institute, Aalborg University LCUBE conference, Vienna 17-18 April 2007

Outline

• A general reduction of CO₂-emission requires, among many other initiatives, a reduction of the heat loss from existing buildings

• Good technical solutions are developed for typical Danish building types

• Solutions for concrete sandwich panel buildings will be presented

• A simple but accurate method for estimating the energy saving is described

U-value requirements in DK

• Thermal bridges often ignored until 2001

• Single glazing formally allowed until 1972

• More severe requirements to light weight walls until 1995

All buildings older than 30 years are completely outdated!

Period walls roof floor slab windows

from 2006 0,2 0,15 0,15 1,5

1995-2006 0,2 0,15 0,2 1,8

1977-1995 0,4 0,2 0,3 2,9

1961-1977 1,0-1,3 0,45 0,45 2,9

EPBD in DK for existing buildings

(EPBD = Energy Performance Building Directive)

The Danish Building Regulations states that:

• When major works are carried out insulation should be improved to today's level for new buildings

• But only if it is profitable to the owner and/or tenants

• And profitability is estimated with quite conservative assumptions regarding service life and interest

Improvement of insulation of existing buildings therefore requires positive engagement of owner and tenants

Concrete sandwich panel buildings

• Main construction type 1960's and 70's in Denmark

• Invented to reduce need for skilled craftsmen

• Similar to many buildings in other European countries

• Insufficient insulation, about 100 mm

• Severe thermal bridges

• Windows worn out

• Roofs needs attention

• Facades not appreciated

• Social problems in neighbourhood

Increased insulation

General problems

• Thicker walls increases depth of window opening reveal and therefore daylight level

• Temporary inconvenience for the tenants Inside insulation:

• Reduces living space

• Risk of condensation in insulation

• Temperature of original structure decreases, which might cause degradation due to moisture

Outside insulation - advantages

• Eliminates most thermal bridges and thereby risk of mould growth

• Living space not reduced

• No need for evacuating tenants during works

• Installations need no change

• Protects original structure

• For concrete sandwich buildings: Unattractive

appearance can be improved

Wall-floor, before,

• Sandwich wall with 80 – 100 mm

insulation

• Reduced insulation along floor

• Water penetration in vertical joints

• Insulation in joints might be missing

Wall-floor, after,

• Outside insulation with vertical studs, wind breaker and rain screen

• Thermal bridge along floor eliminated

• Penetration of rain can be eliminated

Wall-window, before,

• Insulation in wall reduced to 10 mm around window

• Window pane

positioned almost ideally

Wall-window, after,

• New windows

positioned tradition- ally and ideally near to the outside

• Size is increased

• Simple sealing

• 10 mm insulation at end of outer slab and lining of reveal required

Wall-roof 1, before,

• Concrete roof slab with roofing felt and 100-150 mm

insulation

• Connection to wall insulation can be ideal

• Moisture penetration might cause

condensation in roof insulation

Wall-roof 1, after,

• Outside insulation should be connected to roof insulation,

also to avoid condensation

• Original roofing felt acts as water vapour barrier

Wall-roof 2, before,

• Using standard wall element requires separate roof edge

• Corner not insulated

• Severe risk of

condensation and mould growth inside

Wall-roof 2, after,

• Concrete roof edge element removed

• Ideal connection of insulation

• New water vapour barrier at critical spot

Wall-floor slab 1, before,

• Floor slab on ground with 50 – 70 mm

insulation above (or below) the concrete

• Corner not insulated

• Severe risk of

condensation and mould growth inside

• Similar problems if basement

Wall-floor slab 1, after,

• Insulation of plinth 300 mm below

ground surface

• Connects outside and original

insulation of wall

• But direct connection to the ground

Wall-floor slab 2, before,

• Sometimes insulation on outside of plinth, connected to wall insulation

• But direct connection to the ground

Wall-floor slab 2, after,

• Insulation of plinth connects outside and original insulation of wall

• Increased thickness of no importance due to direct connection to the ground

Estimating supplied energy

A major mean for implementing EPBD in Denmark is a PC-programme (Be06), which calculates the need for supplied energy, taking into account:

• transmission loss through the building envelope

• solar gain including shadows

• heat from people and appliances (based on floor space)

• hot water consumption (based on floor space)

• need for cooling if temperatures above 26 °C

• effectiveness of boilers and installations

• solar panels, heat exchangers, heat pumps

• electricity is multiplied by 2.5

Saving of supplied energy after insulation

• Key information for estimating profitability

• Can be calculated with the programme Be06 if the building is modelled before and after the insulation

• Programme required because of influence of eg. solar gain

• Easy general estimation of the saving connected with improvement of each building component wanted, like

?Q_roof = Qroof, original – Qroof, improved

• (eg. should the insulation on the roof be increased by 100 or 200 mm)

Building components

Method for general estimation

• "Typical" building is modelled by the programme before and after insulation

• Sensitivity to change of properties of one building component at a time gives effective heat loss Q

• Increase and decrease gives almost same Q

• Sum of individual changes equals all changes at ones

• ?Q = Q_original - Q_improved

Total supplied energy S kWh

Change

?S, kWh

Effective heat loss Q = ?S /?A kWh/m² Typical building 170 000

Wall area + 200 m² 175 167 + 4833 24,2 Wall area – 200 m² 165 037 – 4963 24,8

Typical concrete sandwich building

• 3 floors

• 12 m x 50 m

• Floor height 2.8 m

• 120 windows 1,5 m x 1,5 m

• 40% North and 60% South

• Ventilation rate 0,7 times per hour

• Details like previous, type 1 where two types

• Effective heat loss can be presented as tables for different constructions before and after insulation

Example of savings

• Q_window's represent difference between larger numbers

• Negative Q due to Danish rules for attribution loss to components

• 48 kWh/m²= 72 before – 24 after

Insulation thickness Effective heat loss, Q kWh/m² or kWh/m Component Area or

length

Original Improved Original Improved

Total saving kWh/year

Saving per m² floor space kWh/m² Wall 790 m² 80 mm 80+145 mm 42,0 12,6 23226 12,9 Floor edge 248 m 80–40 mm 40+145 mm 16,0 2,2 3422 1,9 Windows 270 m² U= 2.7 W/m²K U=1.5 W/m²K 104,9 20,7 22734 12,6 Win. reveal 720 m - 10 mm 25,3 1,1 17424 9,7 Roof 600 m² 100 mm 100+200 mm 34,5 9,8 14820 8,2

Roof edge 1 124 m - - -9,0 0,8 -1215 -0,7

Ground floor 563 m² 50 mm 50 mm 33,4 29,5 2196 1,2

Plinth 1 124 m 0 145 mm 65,2 34,0 3869 2,1

Sum 1800 m² 86476 48,0

Conclusions

• Outside insulation of concrete sandwich buildings from 1960's and 70's can be efficient both regarding durability and energy performance

• The insulation standard can become close to today's requirements by resonable means

• The concept of "Effective heat loss" enables

1. To break down the total energy saving into saving related to each building component

2. To estimate values valid for quite different geometries of buildings based on the same construction technique

Saving of supplied energy after insulation

• Key information for estimating profitability

• Transmission loss and ventilation loss is determined from U-values, degree-days and ventilation rate

• Supplied energy for heating

= transmission loss + ventilation loss – efficiency factor x "free energy"

("free energy" = solar gain + heat form people + appliances)

• Usable "free energy" covers a larger part of the loss after insulation =>

Supplied energy is reduced more than transmission loss